"We believe these allegations regarding Google's search engine practices raise important competition issues," wrote Kohl and Lee, whose committee is already investigating whether Google abuses its power in online search. "We are committed to ensuring that consumers benefit from robust competition in online search and that the Internet remains the source of much free-market innovation."

Representatives from Expedia, Yelp, and Nextag told senators during the Senate Judiciary Committee's antitrust subcommittee hearing in September that the Web giant "doesn't play fair" and "rigs" search results.

Google Executive Chairman Eric Schmidt appeared at the hearing to deny the accusations, and during a tense hearing, Lee tried hard to pin down Schmidt on why results from searches on 650 different products seemed to look fishy. "You've cooked it so that you're always third," Lee said, to which Schmidt responded: "Senator, let me say that I can assure you we haven't cooked anything."

Google fields more than 65 percent of Internet searches in the U.S., according to ComScore market research, and that domination has led to increased scrutiny of the company over the past several years.